This invention relates to a high dielectric ceramic composition, particularly to a laminated ceramic capacitor which has widely been used in an electronic circuit, etc. to be used in an electronic device such as a communication device, an electronic computer, a television receiver, etc. As such laminated ceramic capacitor, preferred are those which are small sized, show a large capacity and have good temperature characteristics.
To obtain a laminated ceramic capacitor with a small size and a large capacity, comprising a ceramic composition with a high dielectric constant and a small temperature dependent capacity (TCC) ceramic compositions are known comprising BaTiO.sub.3 as a main component and a bismuth compound such as Bi.sub.2 O.sub.3 --TiO.sub.2, Bi.sub.2 O.sub.3 --SnO.sub.2, Bi.sub.2 O.sub.3 --ZrO.sub.2, etc. being added thereto. Also known are those compositions which mainly comprise BaTiO.sub.3, to which a bismuth compound, MgO and SiO.sub.2, etc. are added as additives.
However, such a conventional ceramic composition is low in the dielectric constant, having typical values of 1000 to 2000. When the dielectric constant at normal temperature is enhanced, the temperature dependent capacity (TCC) becomes large, and the dielectric losses also become large. A bismuth compound which is added for preventing change of capacity as a function of temparature (TCC) causes unevenness in the composition due to evaporation of Bi.sub.2 O.sub.3 when sintering so that the electronic characteristics of the ceramic composition are fluctuating. Moreover, there exists the inconvenience that Bi.sub.2 O.sub.3 and Pd or Pd--Ag, which are used for inner electrodes for forming a laminated ceramic capacitor, react with each other.In principle, it could be helpful to use Pt as material for the inner electrodes, since Pt does not react with Bi.sub.2 O.sub.3. However Pt is extremely expensive.
On the other hand, Japanese Laid-Open Patent Application No. 57-92575 discloses a ceramic composition having a high dielectric constant which mainly comprises BaTiO.sub.3, to which Nd.sub.2 O.sub.3, Nb.sub.2 O.sub.5, SiO.sub.2, MnO.sub.2 and an oxide of Co are added as an additive without using a bismuth compound, as a material having a high dielectric constant and good temperature characteristics.
In the ceramic composition group having a high dielectric constant disclosed in the Japanese Laid-Open Patent Application No. 57-92575, the temperature dependency of a dielectric constant is good, varying less than .+-.15% in the temperature range of -55.degree. C. to +125.degree. C. However, the dielectric constants do not yet exceed 4000. On the other hand, a laminated ceramic capacitor preferably should satisfy X7R characteristics defined by the EIA standard. The capacity of capacitors answering the X7R characteristics varies less than .+-.15% over a wide temperature range of -55.degree. C. to +125.degree. C. when the electrostatic capacity at +25.degree. C. is a reference.